Field of the Invention
The present invention relates to a sealing system for preventing blood from coagulating on moving parts in an artificial internal organ, such as an artificial heart or pump-oxygenator, in which blood is circulated and which is provided with a mechanical sealing system such as a shaft sealing system.
More specifically, the present invention relates to a sealing system in which a sealing solution is fed at a minute flow rate to that portion of the system which is in contact with blood, thereby preventing coagulation of blood in the system, the sealing solution being loaded with a substance capable of preventing the blood coagulation.
An artificial internal organ, such as an artificial heart, comprises a pump system for feeding blood and a drive system for driving the pump system. If the pump system is of an axial-flow type or centrifugal type, its propeller or impeller is rotated by means of a motor or the like through the drive shaft. In this arrangement, the drive shaft is provided with a sealing system for liquid-tight sealing, and is touched by blood.
Thus, blood gets into a space between moving parts of the shaft sealing system, and then coagulates therein. In some cases, therefore, the sealing system may suffer malfunction due to cohesion or the like, possibly stopping the rotating of the drive shaft.
In some conventional shaft sealing systems of this type, a sealing solution chamber is defined on one side, and is continually filled with a sealing solution so that blood can be prevented from getting into the system by the sealing solution. In general, a physiological saline is used as the sealing solution.
Even in this case, however, blood cannot be securely prevented from getting into the shaft sealing system. It is necessary, therefore, to provide means for preventing blood from coagulating in the system. These circumstances and requirements are common to pump-oxygenators and other artificial internal organs in which blood is circulated and which are provided with a mechanical sealing system, as well as artificial hearts.
In one such means for preventing blood coagulation in the sealing system, the sealing solution in the system is loaded with an anticoagulant such as heparin. This means cannot, however, produce any positive effect, since the anticoagulant action of heparin causes antithrombin III to suppress the activity of thrombin, thereby preventing fibrinogen in blood from changing into fibrin. However, blood in the shaft sealing system of this type, e.g., in a narrow gap between rotating and stationary members of a dynamic-pressure sealing system which doubles as a bearing, is subjected to a substantial shear deformation, and in some cases, may be locally heated to a high temperature of 50.degree. to 70.degree. C. Accordingly, blood may possibly coagulate in a mechanism different from the ordinary mechanism of blood coagulation. Thus, the blood coagulation cannot be effectively prevented by only suppressing the thrombin activity.
The present invention has been contrived in consideration of these circumstances, and a first object of the invention is to provide a sealing system in which an agent for preventing coagulation of blood is loaded into a sealing solution, thereby effectively preventing blood from coagulating in the sealing system. A second object of the invention is to provide a sealing system capable of securely preventing blood coagulation under various possible conditions. A third object of the invention is to provide a sealing system capable of maintaining a preventive effect against blood coagulation for the longest possible period of time.